1. Field of the Invention
The present invention relates to an image pickup device equipped with an image pickup element such as a CCD (charge coupled device) of an interline structure with a function of reading all the pixels.
2. Related Background Art
The image pickup device of a large pixel number, suitable for use in an electronic still camera of a high resolution or the like, is generally represented by a CCD image sensor of interline structure. Such CCD image sensor is provided, as shown in FIG. 37, with photoelectric converting elements (pixels) 101 arranged in a matrix and adapted to convert the incident light into electric charges; vertical charge transfer units (VCCD) 102 for reading the charges accumulated in such pixels 101 and transferring the charges in the vertical direction; a horizontal charge transfer unit (HCCD) 103 for transferring the signal charges, transferred from the VCCD's 102, in the horizontal direction; and an output unit 104 for outputting the transferred signal charges as an image signal from an output terminal 105.
Such interline CCD image sensor functions in the following manner. At first, the signal charges accumulated in the pixels 101 by photoelectric conversion are transferred to the VCCD's 102, and then transferred in succession to the HCCD 103, in case of the illustrated 4-phase drive, by driving pulses φV1, φV2, φV3 and φV4. Then, in the HCCD 103, the signal charges of a horizontal row, transferred from the VCCD's 102, are transferred in succession to the output unit 104, in case of the illustrate 2-phase drive, by driving pulses φH1 and φH2. The signal charges transferred to the output unit 104 are converted into an image signal (voltage) and outputted from the output terminal 105.
FIG. 38 is a block diagram in case the above-explained CCD image sensor is applied to an image pickup device provided with the exposure control function. The image pickup device is composed of a lens and a diaphragm therefor (not shown); an image pickup element 111 consisting of the above-explained interline CCD image sensor; a drive circuit 112 for the diaphragm and the image pickup element 111; a signal processing circuit 113 for applying a necessary process to the image signal; an image memory 114 for temporarily storing the image signal of all the pixels outputted by an image taking operation of the image pickup element 111; an image display unit 115 composed of an electronic view finder or a liquid crystal display for displaying an image constructed from the image signal; and a synchronization control circuit 116 for controlling the entire image pickup device.
In the following there will be explained the function of the image pickup element of the above-explained configuration. At first the light, adjusted to an adequate light amount by the diaphragm, enters the image pickup element 111 and is photoelectrically converted into an output image signal in the image pickup element 111 by the function of the drive circuit 112 under the control of the control circuit 116. Then the level of the image signal is controlled under the control of the synchronization control circuit 116 according to the signal level of the image signal, or the diaphragm is adjusted by the drive circuit 112. Subsequently the image signal is subjected to a necessary processing in the signal process circuit 113 and is stored in the image memory 114. Then the image display unit 115 constructs and displays an image according to such image signal.
In case the image display unit 115 has a number of pixels in the vertical direction, smaller than the number of pixels that can be outputted from the image pickup element 111 in a single photographing operation, the display can be achieved by storing the image signal outputted from the image pickup element 111 in a single image taking operation in the image memory 114 and outputting such image signal to the image display unit 115 after thinning-out the pixel rows to a pixel number in the vertical direction same as that of the image display unit 115, or thinning-out the image signal, obtained by a single image taking operation of the image pickup element 111, by means of the image process unit 113 to a pixel number in the vertical direction same as that of the image display unit 115, then storing the thinned-out image signal in the image memory 114 and outputting such image signal to the image display unit 115.
However, in such conventional image pickup device, if the image pickup element is combined with an image display unit of which the number of pixels in the vertical direction is less than that outputted from the image pickup element in a single image taking operation, the image pickup element is always required to output the image signal of all the pixels that can be in a single image taking operation, so that there is not only required a long time for each image taking operation but, in case of displaying the images in succession for image recording into and reading from the image memory the renewal of the image takes a long time so that it becomes difficult to determine the image configuration.
Also, since the number of pixels in the vertical direction is different between the image pickup element and the image display unit, there are required an image memory and vertical thinning-out means for achieving the synchronization with the image display unit, whereby the circuit configuration becomes complicated and the production cost increases significantly.